In the prior art there is disclosed various automatic door opening systems for garages and for vehicle transport box-like container bodies. Such a mechanism is for example disclosed in U.S. Pat. No. 5,056,847 granted on Oct. 15, 1991. In that patent there is described a system which is quite complex in construction and which is operated from a single side of the door by a fairly large reversible electric motor which is mounted vertically along a side wall of the container. The fact that the motor and drive are located on one side of the door causes an imbalance of the load which may cause the door to jam in the track. Also, the motor occupies space which may interfere with the loading and unloading of cargo and therefore is a nuisance and can result in damage to the cargo or the motor. The motor is also exposed to the cargo and can be damaged during transport by shifting cargo when the vehicle is driven over rough roads. These systems are also not practical for installation and maintenance.